Were you both a cynic and working in Downing Street (the combination is surely possible), you might want Labour to win the Stoke-On-Trent Central by-election.  Such a result would help to shore up Jeremy Corbyn a bit, which would be in the Conservatives’ interest for the time being.  The aim would be to keep the Labour leader on electoral life support until 2020, rather than put him out of his misery before then, and see him replaced by a more effective leader.

Or you might actually hope that Paul Nuttall, who is apparently set to stand as his party’s candidate in the seat, snatches the seat off Labour instead – on the ground that such a result would do even more to destabilse the Official Opposition than a Conservative win.

You might then go on to conjecture that there are lots of seats, in the Midlands and North especially, in which UKIP is a good second and the Tories a poor third, and that the Conservatives and UKIP can divide the country up between them – consigning Labour to oblivion.

Whatever else may be said of that last view, it isn’t consistent with electoral facts.  UKIP’s best performance against Labour in the 2015 election was in Heywood and Middleton (building on the back of the 2014 by-election in that constituency), where it took 32 per cent of the vote and came some 6000 votes ahead of the Conservatives.  The same pattern held in Rotherham, where UKIP’s percentage of the vote was a bit lower, but its lead over the Party a bit higher.

However, these seats were unusual.  In Dagenham and Rainham, UKIP’s third best result, the Tory vote was only some 2500 lower than that of the purple party.  In Rother Valley, the next one down, the gap was about 3000.  In Hartlepool, the next, the difference was similar.  In the next still, West Bromwich West, it was about 500.

In other words, there are very few seats where UKIP is breathing down Labour’s neck and the Conservatives are nowhere near UKIP.  It can be argued that Nuttall’s party will do much better against Labour in 2020.  If this turns out to be the case, it will draw on two main sources of votes (assuming similar turnout).  The first is Labour voters.  But a Brexit-delivering Tory party will also be in the hunt for some of these.  The second is Conservative voters.  But why would the Party want to abandon these to UKIP in seats where it is on their tail?

No serious party will throw all its energy into all seats at once: indeed, the Lynton Crosby-led Tory campaign of 2015 showed the benefits of targetting.  It can be assumed that, come 2020, CCHQ will not be focusing on trying to win Hartlepool or West Bromwich West.

But the practical case (let alone the broader political one) for simply abandoning these seats to UKIP altogether is very slim.  Perhaps the moral is not to assume anything about turnout in 2020, after all.  The turnout in the 2015 general election was 66 per cent.  Last June, it was 72 per cent.

Were it to be nearer the 2016 than the 2015 figure in 2020 and were Labour’s support to fall – a double assumption, to be sure, but not a far-fetched one – the interplay between Labour, the Conservatives and UKIP in some Labour-held seats could be very complex indeed.

At any rate, cynicism has its limits, like almost everything else. Neither Number Ten nor CCHQ will want to write off Stoke-On-Trent Central, where the Party came only 33 votes behind UKIP in 2015.